The present invention relates to a slotted antenna.
PCT Publication No. WO97/41619 describes a combination flat antenna which combines a mobile radio antenna for an operating frequency of 900 MHZ and a GPS antenna (global positioning system). The mobile radio antenna is composed of a circular electrically conducting disc which is supplied with power at its midpoint and is situated above an electrically conducting base area. The circular disc is connected to the base area by three electrically conducting webs at the outside edge of the disc. This results in three slotted antennas arranged in a circle. The GPS antenna is designed as a patch antenna and is situated on the circular disc so that the two antennas may be combined in one compact design.
The slotted antenna according to the present invention has the advantage over the related art that the first disc includes a recess; a second electrically conducting disc is situated above the recess and is connected at its outer edge to the first disc by at least one second electrically conducting web; and an antenna conductor leads to the second disc. This makes it possible to implement a cascaded slotted antenna which requires only a single common feed via the antenna conductor. Thus, it is possible to manufacture a radio antenna for two or more frequency ranges in an efficient and space-saving design. A GPS patch antenna may be additionally situated on the second disc. Because of the supplementation according to the present invention of the slotted antenna known from the publication cited above by adding at least one extra resonator, it is possible to stack a plurality of such resonators in a compact design. approximately circular perimeter. In this way, an omnidirectional diagram without a preferred direction may be implemented as the directional characteristic of the slotted antenna.
One advantage is also that at least one of the discs is designed not with a circular perimeter but instead in the form of an n-sided, oval, elliptical or asymmetrical shape, for example. This yields a distorted directional characteristic having preferred directions for the slotted antenna. This distortion of the directional characteristic may be used in a controlled manner for compensation of ambient influences. Thus, for example, distortion of the directional characteristic of such a slotted antenna situated on a motor vehicle due to struts or roof edges of the vehicle may be counteracted so that an approximately omnidirectional diagram without preferred directions is again obtained with the superpositioning of the distortion formed by the selected shape of the discs on the distortion due to the struts or roof edges.
Another advantage of discs designed to have a circular perimeter is that the circular area of the recess of the first disc is smaller than the circular area of the second disc. In this way, with a concentric arrangement of discs and the recess and with webs situated perpendicular to the discs, a flatter emission in the elevation radiation diagram may be implemented. Due to a concentric arrangement of the two discs, it is possible to implement concentric directional characteristics for the resonators based on the two discs.
It is especially advantageous that three webs are situated between the first disc and the base area, and three webs are likewise situated between the first disc and the second disc. In this way, each of the two resonators is designed as a multiple slotted antenna which implements a relatively high transmission and/or reception bandwidth.
It is especially advantageous that the webs between the base area and the first disc are mutually rotated by 60xc2x0 with respect to the webs between the first disc and the second disc. This minimizes any mutual influence of the two resonators. Then the current and voltage peaks occurring at the resonators do not coincide but instead are offset electrically by 180xc2x0. Therefore, this yields a current assignment which permits good emission at the operating frequency of each of the two resonators.
It is especially advantageous that at least one third disc, which also includes a recess, is provided between the first disc and the second disc; the third disc is connected to the outside edge of the directly adjacent disc above it by at least one third web which corresponds in particular to the at least one second web and is connected to the directly adjacent disc beneath it by at least one fourth web at its own outside edge. This permits implementation of a slotted antenna having more than two resonators, each being resonant in a different frequency range, so that a multi-band antenna having more than two frequency ranges for emission and/or reception of signals may be implemented. A compact and space-saving design is possible by stacking the resonators one on top of the other.